A Guide to EGR Valve Operation and NOx Reduction

Understanding the EGR Valve Operation and Its Importance

The Exhaust Gas Recirculation (EGR) valve plays a critical role in reducing harmful emissions and improving engine efficiency. Despite its significance, many vehicle owners are unfamiliar with how the EGR valve operates, what it does, and what happens when it fails. This article provides a detailed overview of the EGR valve operation, including its purpose, activation conditions, and common failure modes.

What Does the EGR Valve Do?

The primary function of the EGR valve is to reduce combustion temperatures to reduce the formation of nitrogen oxide (NOx) emissions, which are harmful pollutants that contribute to air pollution and smog. NOx gases are produced during the combustion process, particularly at high temperatures. The EGR valve helps lower the combustion temperature by recirculating a portion of the engine’s exhaust gases back into the intake manifold. This dilutes the air-fuel mixture entering the combustion chamber, reducing the peak combustion temperature and, consequently, the formation of NOx emissions.

In addition to reducing emissions, the EGR valve can also improve fuel efficiency by optimizing the combustion process. By controlling the flow of exhaust gases into the intake manifold, the EGR valve helps maintain the ideal combustion temperature and pressure, leading to more efficient fuel usage.

How Does the EGR Valve Work?

The EGR valve operates by opening and closing to control the flow of exhaust gases into the engine’s intake manifold. There are two main types of EGR valves: vacuum-operated and electronically controlled. While both types serve the same purpose, their mechanisms differ slightly.

Vacuum-Operated EGR Valve— In older vehicles, the EGR valve is typically vacuum-operated. The valve is connected to a vacuum source from the intake manifold or a vacuum pump. When the engine is under load or at higher RPMs, the vacuum signal causes the EGR valve to open, allowing exhaust gases to flow into the intake manifold. When the engine is idling or under light load, the vacuum decreases, causing the EGR valve to close.

Electronically Controlled EGR Valve— In modern vehicles, the EGR valve is usually electronically controlled by the engine control unit (ECU). The ECU monitors various engine parameters, such as throttle position, engine speed, and temperature, to determine when and how much the EGR valve should open. An electric solenoid or motor controls the valve’s position, allowing for more precise regulation of exhaust gas flow compared to vacuum-operated systems.

Regardless of the type, the EGR valve only operates under specific conditions. It typically opens when the engine is warm, under load, and running at part throttle. At idle or full throttle, the EGR valve remains closed to prevent excessive recirculation of exhaust gases, which could negatively impact engine performance and drivability.

EGR Valve Operation: When Does the EGR Valve Allow Exhaust Flow?

EGR valve operation is contingent on the engine’s operating conditions. The ECU continuously monitors the engine’s status and opens or closes the EGR valve as needed. Generally, the EGR valve operates under the following conditions:

Not During Engine Warm-Up— The EGR valve is closed during the engine warm-up.
Not During Idle and Full Throttle— At idle and full throttle, the EGR valve is closed.
Yes, During Part Throttle Operation— It’s open during cruising at a steady speed
Yes Under Heavy Load— Heavy loads produce the most heat and that heat can cause NOx and detonation (knock)

Diesel EGR valve

Diesel engines produce far more soot than gasoline engines. So modern diesel vehicles employ a diesel particulate filtration system to remove the soot. If the soot-laden exhaust is routed directly into the combustion chamber, it can mix with oil vapor and form sludge. To prevent that, a high-pressure EGR valve is used to divert the high-flow, high-soot exhaust gas to the diesel particulate filter first before it enters the combustion chamber. The filtered exhaust gas is then passed back to the inlet manifold either via a pipe or internal drillings in the cylinder head.  A secondary valve is also used to help create a vacuum in the inlet manifold, as this is not naturally present on diesel engines.

What is an EGR delete

Powersports enthusiasts often remove the EGR valve and cover the port with a metal plate. They figure that since EGR reduces the amount of air and fuel entering the engine, the EGR system costs them some performance. This is flawed reasoning.

Why an EGR delete doesn’t help increase performance

The entire reason for EGR is to reduce combustion temperatures to eliminate detonation and reduce NOx formation. So the EGR valve is only open at part throttle and then again when the engine is under heavy load.

If you put the pedal to the metal from part throttle to get more power, the EGR opens. This is when your engine is most at risk for detonation due to the extremely high combustion temperatures. So, deleting your EGR valve puts your engine at risk.

Deleting Your EGR Doesn’t Really Get You The Power You Think it Does

In Reality, you’ll get:

• Minimal power gains: Any power increases are usually minimal, often in the range of 5-15 horsepower at most and only when you put the pedal to the metal. In other words, these gains are typically only noticeable at higher RPMs.
• Inconsistent fuel economy: While some report slight improvements, others experience decreased fuel efficiency due to altered combustion temperatures and air-fuel ratios.
• Engine stress: The EGR system helps control combustion temperatures. Without it, engines may run hotter, potentially leading to detonation damage and increased wear over time.
• Emissions increase: EGR deletes almost always result in increased NOx emissions, which can cause issues with other engine components and emissions tests.
• Vehicle-specific results: Effects can vary greatly depending on the specific vehicle and engine design. What works for one vehicle may not work for another.
• Modern engine incompatibility: Many modern engines are designed with EGR systems as an integral part. Removing them can significantly disrupt engine management and performance.

EGR trouble codes

How an EGR valve fails

EGR valves operate in a high-heat hostile environment. Exhaust gas contains soot and unburned fuel. Over time the valve pintle and seat can accumulate carbon buildup that prevents the EGR from fully closing. The carbon buildup can also cause pintle binding, preventing full or partial opening/closing.

Carbon buildup can also occur in the exhaust manifold and intake manifold passages, reducing EGR flow.

When passages clog or the valve can’t fully open or close, the expected exhaust flow doesn’t match the commanded exhaust flow. When that happens, the PCM sets a trouble code.

Signs of EGR valve failure

Check engine light— When passages clog or the valve can’t fully open or close, the expected exhaust flow doesn’t match the commanded exhaust flow. When that happens, the PCM sets a trouble code.

Engine performance issues: if the EGR valve sticks open, the exhaust flow will dilute the air/fuel mixture to the point where it affects engine performance. So you can experience reduced power, poor acceleration, and rough idle. It may also produce turbo boost pressure leaks, causing the turbo to work harder.

Increased NOx emissions — A stuck-shut EGR will cause you to fail an emission test due to higher than-allowed production of NOx.

Engine knock— the higher temperatures and NOx may also result in increased detonation or knock, heard as knocking noises in the engine.

Common EGR fault codes

On late-model EGR valves the following fault codes are common:

P0400: EGR flow malfunction. When the PCM commands EGR, it expects to see the results in engine RPM and O2 sensor readings. If the results don’t match expectations, the PCM sets a P0400 trouble code.

P0401: EGR insufficient flow detected—This might be caused by carbon buildup in the exhaust passages or a buildup in the EGR valve.
P0402: EGR excessive flow detected— This is most often caused by a partially or fully stuck open EGR valve.
P0403: EGR circuit malfunction—In an electronically controlled EGR valve, this can indicate a short to ground, open, or excessive coil resistance.
P0404: EGR circuit range/performance—In an electronically controlled EGR valve, this can indicate a short to ground, open, or excessive coil resistance.

Sensor range codes refer to the sensors used to measure how far the pintle has moved. A sensor range code indicates a problem between the commanded movement versus actual movement.
P0405: EGR sensor A circuit low—
P0406: EGR sensor A circuit high
P0407: EGR sensor B circuit low
P0408: EGR sensor B circuit high
P1403: EGR solenoid low
P1404: EGR system – closed valve pintle error
P1405: EGR solenoid high
P1406: EGR system pintle position error

©, 2021 Rick Muscoplat